1. Field of the Invention
The present invention relates to the intimate contacting or admixture of a plurality of distinct physical phases, and plural phase contactor therefor; more especially, the invention relates to the intimate contacting of plural, distinct physical phases and ultimate separation of the various products resulting from such admixture.
2. Description of the Prior Art
A great variety of gas/liquid, and other phase contactors, mixers or separators, whether of pneumatic, mechanical, or other type, are of course well known to the state of this art. Equally well known, on the other hand, is the art appreciation of the various difficulties that are encountered in attempting to disperse, disintegrate, concentrate, comminute or pulverize, e.g., a liquid in a gaseous environment or treatment phase, such as, for example, effecting the drying of certain liquid materials through a spray drying technique. An ideal dryer of this type would comprise a vertical, cylindrical contact zone in which the gas and the dispersed liquid droplets are uniformly, regularly distributed, with the liquid being dispersed or entrained therein in the form of substantially equally sized droplets. Ideally, all of the droplets would follow the same flow path through the apparatus as to be subjected to the same treatment and, accordingly, to continuously give rise to the formation of identical product. Stated differently, the entire volume of the physical phase to be treated, in this spray drying example the same being a dispersed liquid droplet phase, should be subjected to the same historical profile operationally in order to receive an essentially identical amount and duration of treatment by the treatment medium or phase, under the same conditions [especially those of temperature and concentration]. And the immediately aforesaid of course presupposes or implies the realization or attainment of a precisely, indeed near perfectly controlled rate of flow.
In the aforenoted, commonly assigned copending application, Ser. No. 916,477, filed June 19, 1978, it has been shown that certain conditions very close to the ideal can be attained by insuring flow or distribution of vortex type, by operating within certain well defined parameters of both geometry and kinetics. As disclosed in said application Ser. No. 916,477, in an initial stage in the process the plural phases are manipulated upstream of their convergence by supplying same to a cylindrical distribution zone, at least one of the phases being introduced via a helical trajectory inducing inlet and being axially extended, while maintained in an axially symmetrical, helical flow path, through said distribution zone. By "axially symmetrical, helical flow path", through said distribution zone. By "axially symmetrical, helical flow path", there is denoted a regularly repeating, helical path of axially extending downward flow which is essentially symmetrical with respect to at least one plane including the axis of such helical flow. At least one other phase is also introduced to the distribution zone, via suitable inlet and it too is axially extended therethrough, but in this instance the path of downward flow is essentially rectilinear and proceeds at a speed of from 0.03 to 3 m/sec. The longitudinal axis of the path of rectilinear flow is, moreover, coaxial with the longitudinal axis of the path of helical flow. The current of circulating helical flow next progresses to a confining zone of restricted flow passage so constructed that the minimum momentum of the helical flow is at least 100 times greater than the momentum of the coaxial rectilinear flow, and such that the plural flow paths or separately supplied phases converge and are combined, blended and admixed in yet a third distinct zone, the contact zone. Thus, the trajectory imparted by the helical flow, at its point of exit from the zone of restricted flow passage, forms one of the classes of generatrices of a hyperboloid to a thin surface, or, more correctly, a layered stack of a plurality of hyperboloids. Said generatrices are conveyed through a series of circles to form a ring of narrow width which is situated downstream of the restricted passage for the helical flow, but upstream of its divergence. This ring surrounds or circumscribes a zone of depression, the effects of which are manifested both upstream, on the phase constituting rectilinear flow, as well as downstream, on the phase constituting circulating helical flow, by effecting the recycling of a portion of such fluids. In this fashion, in the zone downstream from the area of combining or convergence of the separately supplied fluids or plural flow paths, and in the same plane which is perpendicular to their coaxis, all vectors of velocity of the individual elements constituting total volume are equal in absolute value, are divergent and are mutually subtracted upon rotation about the coaxis; hence, at two successive intervals, two distinct units of volume in the same trajectory evidence the same historical processing profile, thus assuring maintenance of contact between the two phases. Accordingly, if the rectilinear flow, for example, be constituted of a liquid phase and the helical flow of a gaseous phase, the liquid phase will be disintegrated, fractionated or atomized into a multitude of droplets, with each droplet being dispersed in a given volume of the gas and subjected to a certain movement or velocity thereby, by being physically swept along with said gas, thus creating the effect of centrifugation; this phenomenon enhances contact with the vector gas and, in those cases where combustion results, insures ignition and flame stability. Such a process, therefore, is a notably marked advance in the art of rapid intimate contact between, and ultimate separation of, two disparate phases. Indeed, such process is eminently well suited for the treatment of highly thermally sensitive materials with very hot gases. For example, milk [which should not be heated to a temperature in excess of about 80.degree. C.] can conveniently be dried with gases as hot as 500.degree. C. without undergoing deterioration or degradation. And an added advantage of this process is that such operations as drying and evaporation can be carried out in high energy yield, in minimum space requirement installations. Nonetheless, a product separation problem arises, for example, the elimination of gases from any solid or liquid phase recovered. As another example, like phase separation difficulties were encountered in attempting to concentrate such acids as sulfuric and phosphoric. In the aforementioned application, Ser. No. 916,477, this function of separation was attempted to be assured by means of a cyclone. Unfortunately, though, such a device has considerable space requirements and if it be necessary that a predetermined efficiency be attained, utilization of such a device fosters a substantially cost increase, even without taking into account energy loss. Mofidication of the cyclone itself has also been proposed to alleviate such problems, for example, by placing helical guide vanes or the like inside the cyclone. But, as can be seen from, e.g., Perry and Chilton, Chemical Engineers' Handbook, 5th Edition, pp. 20-86, McGraw-Hill Book Co., such vanes or the like, when placed inside the cyclone, will have a detrimental effect on performance of the unit because of reduced pressure throughout and a correspondingly even greater reduction in collection, or product recovery, efficiency.
Thus, it was proposed, in copending application, Ser. No. 013,295, that if a cylindrical wall member be integrally secured to the trajectories or outlet of the contact zone of any device disclosed in the Ser. No. 916,477 application, and an abrupt change or variation in the velocity field of at least one of the plural phases be effected thereby, while at the same time maintaining the general direction of flow of said phases, excellent phase separation is obtained, even though a device of but small dimensions is used and without encountering those inconveniences or disadvantages which result from the modification of the known and classical cyclones by insertion of helical guide vanes or the like.
More particularly according to the invention disclosed and claimed in said application Ser. No. 013,295, there are characterized both apparatus and process for the formation of an intimate, homogeneous product mix comprising at least two disparate physical phases, and for the ultimate facile separation and recovery of the various products resulting from such mixing. Consistent with such invention, an intimate, homogeneous admixture of said phases is assured by mutually contacting the same by means of a flow of vortex type. This is accomplished by supplying at least one of the phases to a first cylindrical distribution zone via a helical trajectory inducing inlet, and whereby the same is axially extended through such zone while being maintained in an axially symmetrical, helical flow path. By "axially symmetrical, helical flow path", here too is intended a regularly repeating, helical path of axially extending downward flow which is essentially symmetrical with respect to at least one plane including the axis of the helical flow. At least one other phase is also introduced to this first distribution zone, via suitable inlet, and it too is axially extended therethrough, but in this instance the path of downward flow is essentially rectilinear. The longitudinal axis of the path of rectilinear flow is, moreover, coaxial with the longitudinal axis of the path of helical flow. The current of circulating helical flow next progresses to a confining zone of restricted flow passage so constructed that the minimum momentum of the helical flow is at least 100 times greater than the momentum of the coaxial rectilinear flow, and such that the plural flow paths or separately supplied phases converge and are combined, blended and admixed in yet a third distinct zone, the contact zone. In the contact zone, the trajectories common to the different phases are directed against a cylindrical surface, the intimate admixture remaining in contact with said surface as a result of the effects of that centrifugal force imparted to the system by means of the circulating, helical flow. Phase separation is next effected by an abrupt change in the field of velocities of at least one of the disparate phases, while at the same time maintaining the general direction of flow of the several phases. Ultimately, the products resulting from the intimate admixture or contacting of the various phases are recovered separately. The plural phases subjected to treatment according to the application Ser. No. 013,295 may be either gaseous, liquid or solid phases. For example, the concentration of a gas/liquid admixture is readily effected, as are (i) the drying of a gas/solid mixture, (ii) the decantation of two immiscible liquids, and (iii) the absorption washing of a gas with a liquid; the invention of the application Ser. No. 013,295 is particularly worthwhile for the single step concentration [vis-a-vis the two-stage concentrations characterizing the then state of the art] of dilute solutions of phosphoric acid.
Unfortunately, though, in certain instances, due to the presence of a variety of impurities, processes carried out in consonance with the teachings of the application Ser. No. 013,295 proceed only difficultly. For example, in attempting to concentrate residual acidity deriving from the manufacture of titanium pigments, the presence of iron, typically manifested by the formation of iron salts, markedly detracts from process efficacy.